1. Field of the Invention
The present invention generally relates to a probe device and a method for a continuous measurement of oxygen in molten metal, and particularly, it relates to a prove device and a method for continuously measuring over a relatively long time interval a quantity of oxygen in a running body of molten metal such as of copper.
2. Description of Relevant Art
In production, such as of a copper wire, employing a continuous casting and rolling method, there usually is observed a tendency for a body of molten metal for a continuous casting to have a violently varying oxygen concentration. There is thus needed, in the casting, a measurement of oxygen concentration to be continuously performed to ensure a secured quality in articles. For such a reason, there have been proposed various probes for measuring an oxygen concentration in molten metal.
For example, Japanese Utility Model Publication No. 63-11646 has disclosed an oxygen continuous-measuring probe in which a solid electrolyte tube has at a close end thereof a temperature moderating layer of an identical electrolyte material, a reference electrode for use in detection of an electromotive force (hereafter "emf") representative of an oxygen concentration in a body of hot atmosphere or molten metal, and a thermocouple installed in the reference electrode for detecting a varying temperature of the body.
Japanese Utility Model Publication No. 2-40536 has disclosed a probe for measuring an oxygen concentration in molten metal, in which a solid electrolyte tube has an exposed close end part thereof protected by a filter formed with a multiplicity of sufficiently small perforations for completely preventing a slag invasion, permitting part of molten metal to soak therethrough. The filter may be cooperative with an external protection tube to constitute a totally enclosing protector. However, in a concerned field of art, this probe has a limited application to a relatively short measurement, because of a possible blocking due to binding slag in a continued use.
Further, FIG. 1 shows another conventional probe for measuring a quantity of oxygen in molten metal. As shown in FIG. 1, the conventional probe has in a radially central portion thereof a solid electrolyte tube 73 close at a lower end. The close end of the electrolyte tube 73 is connected at the inside to a lead 74 such as of a platinum wire. Provided around a wall of the tube 73 is an external protection tube 71 that protects tube 73 and serves as an external electrode. A lower part of the solid electrolyte tube 73 is fixed inside the external protection tube 71, with a binding body 72 of fixative material such as a refractory cement filled therebetween. A voltmeter 79 is connected between an upper end of the protection tube 71 and one end of the lead 74 of which the other end is connected to the lower end of the electrolyte tube 73.
The probe of FIG. 1 has a body of fixative material filling inside the lower part of protection tube 71, as described. Such an oxygen measuring probe will be called "type A".
In the A-type oxygen measuring probe of FIG. 1, the solid electrolyte tube 73 is supplied with a body of reference gas, such as of air or oxygen gas or as a gaseous mixture containing oxygen, having a known concentration of oxygen. As a measuring lower end part of the probe is dipped in a body 75 of molten metal, there is constituted an oxygen concentration cell with the reference gas working as a reference electrode having a known oxygen partial pressure, generating an emf between inner and outer surfaces of the solid electrolyte tube 73, which emf is measured by the voltmeter 79 connected between the lead 74 and the external protection tube 71, permitting an oxygen concentration of the molten metal 75 to be calculated.
FIG. 2 shows another conventional A-type oxygen measuring probe that has been disclosed in Japanese Utility Model Application Laid-Open Publication No. 57-42947. In the conventional probe of FIG. 2, a solid electrolyte tube 84 has a body 83 of sintered material filling inside a wall thereof, and a lower end part of an insulating tube 87 fitted therein. The insulating tube 87 has a rod-shaped internal electrode 86 inserted therethrough to be in contact at its lower end with an upside of the sintered material 83. As such the measuring part of the probe is dipped in a body 85 of molten metal, there is generated an emf to be measured by a voltmeter 89 connected between an upper end of the internal electrode 86 and a protection tube 81 as an external electrode.
However, in measurement by the foregoing A-type oxygen measuring probes, a body 72, 82 of fixative material employed for fixation of solid electrolyte tube 73, 84 is dipped in the molten metal 75, 85. Therefore, the fixative material 72, 82 reacts on the molten metal 75, 85, dissolving therein as impurities, thus resulting in a degraded quality of articles produced therefrom. Moreover, in a case the fixative material consists of an insufficiently heat-resistive cement, there develop cracks during continuous measurement, causing molten metal to invade thereinto, giving rise to a system of irregular circuits. As a result, the conventional A-type probes tend to suffer from a progressively increasing difficulty of measuring an exact emf, thus having a limited application to very short measurements. Further, the solid electrolyte tube 73, 84 has its lower end projecting under a lower edge of the protection tube 71, 81, which lower end may be easily damaged.
As a countermeasure to such issues, a production line of an A-type oxygen measuring probe is subjected to a sampling inspection at or after a starting of each repeated run of the line, where a sampled article is dipped in molten metal for a limited short time to measure an oxygen concentration therein at intervals of a predetermined period, so that the oxygen concentration is measured a number of times for the inspection, before a necessary disposal of the sampled article. Such a production costs dear. Moreover, in a long-lasting run of the production line, the molten metal employed for the inspection may have a varying oxygen concentration with a difficulty even for an artisan to instantly cope with. Further, such a line is inadaptive for a continuous long production of articles with oxygen contained to some extent for a secured performance.
In addition, to overcome such issues, there has been proposed an oxygen measuring probe (hereafter called "type B") having residual gas in a space defined under a body of fixative material, as shown in FIG. 3. In this figure, a solid electrolyte tube 73 is fixed inside an external protection tube 71, with a binding body 72 of fixative material filled therebetween above a level upwardly off from a lower edge of the protection tube 71, thereby defining a space 76 around a lower end part of the electrolyte tube 73, to have a body of residual gas left therein when the probe is dipped in a body 75 of molten metal. In measurement, an emf is read on a voltmeter 79 connected between an upper end of the protection tube 71 and one end of a lead 74 of which the other end is connected to an inner bottom of the lower end part of the electrolyte tube 73.
Such the B-type oxygen measuring probe is allowed to overcome the discussed issues. However, when a measuring part of the probe is dipped in the molten metal 75, the electrolyte tube 73 yet suffers an unstable contact with the molten metal 75. In particular, when the molten metal 75 flows or runs, the tube 73 has little chance to contact with fresh part or layer of the molten metal 75 that has not been brought into contact, thus failing to exactly measure a continuously varying concentration of oxygen in the molten metal 75.
To overcome such shortcomings of the A-type and B-type probes, there has been proposed another conventional oxygen measuring probe (hereafter called "type C") in Japanese Patent Application Laid-Open Publication No. 55-98351, in which an external protection tube 71 has a slit or thru-hole formed in a lower end part thereof as shown in FIGS. 4 and 5A to 5C. In the C-type oxygen measuring probe shown, a solid electrolyte tube 73 is fixed in position so that its lower end does not project under a level of a lower edge of an external protection tube 71. Moreover, the protection tube 71 has a small space 76 defined inside a lower end part thereof for a body of residual gas to be left there. Further, as best shown in FIGS. 5A to 5C, the lower end part of the tube 71 is formed with a narrow and short slit 77 or a pointed thru-hole 78, as necessary for a stable contact of molten metal 75 with the lower end of the electrolyte tube 73. In measurement, an emf is read on a voltmeter 79 connected between an upper end of the protection tube 71 and one end of a lead 74 of which the other end is connected to an inner bottom of the lower end part of the electrolyte tube 73.
In the conventional C-type probe, the electrolyte tube 73 is allowed to have an improved contact with the molten metal 75 due to an enhanced displacement thereof.
However, in practical application to a runner through which hot, viscous and weighty molten metal runs at a speed toward a continuous casting and rolling section, the C-type probe still has part of molten metal stagnant in the protection tube 71, with occasionally generated and gradually growing cores of slag floating alongside walls of both tubes 71, 73, adversely affecting the emf to be measured, and aggregating in a vicinity of an exit slit 77 or an exit hole 78, partially stopping the slit or hole, with an increased stagnating tendency giving rise to an excessive aggregation, resulting in a failure of effective measurement before an end of a continuous long service.
No slag nor potential slag core nor foreign matter should enter in a protection tube, which has been a common recognition to the artisan. Accordingly, the smaller a front slit or a front hole is set, the better it appears.
Moreover, the lower end part of the protection tube 71 is relatively short so that the body of residual gas left in the space 76 has a limited volume and a limited vertical thickness under normal condition. The thickness becomes still smaller, as the lower end part of the probe is submerged to an increased depth. At a desirable depth, a flattened body of residual gas may be easily broken by an occasional weighty irregular action such as a surfacial protrusion of running molten metal, so that the molten metal may lick the fixative material 72 from time to time.
Further, in each of the foregoing conventional probes, the external protection tube needs a sufficient rigidity to stand, all the way of a continuous long service, with an integration of dynamic pressures substantially over an entire front wall receiving ceaselessly surging streams of weighty molten metal, in addition to that the molten metal is hot enough to make a dipped part of the protection tube gradually flexible or flexed. A necessary wall thickness renders a cost dear, as an employable material is of value.
Still more, in each conventional case described, it is impossible to reuse a dipped member, as so believed in the field of endeavor.